The proposed research seeks further clarification of neural and/or pharmacological mechanisms regulating postnatal ocular growth and influencing the development of refractive errors, particularly myopia (nearsightedness). In chick and mammals including man, vision-dependent feedback mechanisms influence postnatal ocular growth, hence implicating neural mechanisms in the control of refraction. Much evidence identifies the retina itself as exerting the dominant influence on eye growth and refraction, with perhaps some modulation from other components of the nervous system. We seek enhanced understanding of the nature and interaction of the neural mechanisms influencing postnatal eye growth and refractive status. Using the chick as a model, studies will be directed to the following specific aims: 1) define further the cholinergic mechanisms modulating eye growth and refraction; 2) understand the role of light and dark in influencing postnatal eye development; 3) further clarify retinal mechanisms modulating eye growth, emphasizing the role of GABA; 4) establish interactions of the multiple neuroreceptor systems that modulate eye growth; and 5) identify neural mechanisms controlling the shape of the eye and its components, as distinct from axial length and refraction alone. Past research conducted under this grant has impacted significantly in this field: stimulating other research programs; opening possibilities for clinical drug therapies, one of which is now under active study in children; and suggesting novel directions to seek potential risk factors for clinical myopia. We hope that our studies will continue to lead to improved understanding of ocular growth and ultimately towards rational approaches to prevent refractive errors in children.